Training sequence transmission method and apparatus

ABSTRACT

This application provides a training sequence transmission method and apparatus. The method includes: A first AP broadcasts a trigger frame, where the trigger frame indicates a time sequence of separately sending channel sounding frames by N STAs, and N is an integer greater than 1. The first AP receives the channel sounding frames sequentially sent by the N STAs, where one channel sounding frame includes one or more training sequences. In this solution, only one trigger frame needs to be sent, so that the N STAs can be triggered to separately report channel sounding frames to M+1 APs. However, in the conventional technology, each AP needs to send one channel training request to each STA, that is, N×(M+1) channel training requests are sent in total, to trigger each STA to report a training sequence. Therefore, this solution can significantly reduce signaling overheads.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2020/083350, filed on Apr. 3, 2020, which claims priority toChinese Patent Application No. 201910267279.2, filed on Apr. 3, 2019.The disclosures of the aforementioned applications are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

This application relates to the field of mobile communicationtechnologies, and in particular, to a training sequence transmissionmethod and apparatus.

BACKGROUND

The 802.11n standard, the 802.11ac standard, and the 802.11ax standardof the Institute of Electrical and Electronics Engineers (IEEE) allintroduce a multiple-input multiple-output (MIMO) technology at aphysical layer, and spatial multiplexing is used to multiply a systemcapacity and greatly improve performance. The MIMO technology means thata plurality of antennas are simultaneously configured at a transmit end(for example, an access point (AP)) and a receive end (for example, astation (STA)), and signals are sent and received by using differentantennas, so that the system channel capacity can be multiplied by usinga spatial multiplexing gain without increasing a frequency resource andantenna transmit power. A MIMO system can effectively suppress or cancelco-channel interference by using a precoding technology. Theoretically,if there are N antennas at the transmit end, electromagnetic signalsthat do not interfere with each other can be transmitted to N receiveends at the same time, and signals of the plurality of antennas aresuperimposed, to generate optimal spatial joint diversity and performinterference cancellation processing.

A prerequisite for implementing MIMO precoding is that the transmit endhas a training sequence from the AP to the STA. Channel estimation isperformed between the AP and the STA based on the training sequence, sothat orthogonal precoding generated based on the channel estimation canenable user flows to be orthogonal and not interfere with each other.

FIG. 3 is a schematic diagram of a training sequence transmission methodin the conventional technology. In this solution, an AP sends a channeltraining request (TTRQ), and requires a STA to send a null data packet(NDP) frame including a training sequence of an uplink channel based onreciprocity between the uplink channel and a downlink channel (forexample, the uplink channel is equivalent to the downlink channel). TheAP estimates the uplink channel based on the training sequence of theuplink channel in the received NDP frame, to replace channel estimationof the downlink channel between the AP and the STA. In this solution,the AP sends a TRQ to a STA-1. After receiving the TRQ, the STA-1 waitsfor one short interframe space (Short Interframe Space, SIFS) and sendsa training sequence to the AP. Then, the AP may perform estimation on achannel between the AP and the STA-1 based on the training sequence.Then, after waiting for one SIFS, the AP sends a TRQ to a STA-2. Afterreceiving the TRQ, the STA-2 waits for one SIFS and then sends atraining sequence to the AP. Then, the AP may perform estimation on achannel between the AP and the STA-2 based on the training sequence.Then, the foregoing process is repeated until channel estimation betweenthe AP and N STAs are obtained. Similarly, if there are a plurality ofAPs, each AP may repeat operations of the foregoing AP to obtain channelstate information between each AP and each STA through sounding.

The foregoing solution has the following disadvantages: In thissolution, signaling exchange is frequent; air interface overheads arelarge; and as a quantity of APs or a quantity of STAs increases,overheads greatly increase.

SUMMARY

This application provides a training sequence transmission method andapparatus, to reduce overheads of transmitting a training sequence in achannel estimation process.

According to a first aspect, this application provides a trainingsequence transmission method. The method includes: A first access pointAP broadcasts a trigger frame, where the trigger frame indicates a timesequence of separately sending channel sounding frames by N stationsSTAs, and N is an integer greater than 1. The first AP receives thechannel sounding frames sequentially sent by the N STAs, where onechannel sounding frame includes one or more training sequences. Based onthis solution, only one trigger frame needs to be sent, so that the NSTAs can be triggered to separately report the channel sounding framesto the first AP. However, in the conventional technology, an AP needs tosend one channel training request to each STA, that is, N channeltraining requests are sent in total, to trigger each STA to report atraining sequence. Therefore, this solution can significantly reducesignaling overheads.

In a possible implementation, that a first AP broadcasts a trigger frameincludes: The first AP broadcasts the trigger frame to the N STAs and Msecond APs, where the trigger frame further indicates whether the Msecond APs are ready to receive the channel sounding frames sequentiallysent by the N STAs, and M is a positive integer.

In a possible implementation, before the first AP broadcasts the triggerframe to the N STAs and the M second APs, the first AP separately sendsindication information to the M second APs, where the indicationinformation is used to indicate to follow an indication of the triggerframe of the first AP.

In a possible implementation, the first AP receives notificationinformation from a central controller, where the notificationinformation includes identification information of the N STAs, and thenotification information is used to indicate to perform channel soundingon the N STAs.

In a possible implementation, the notification information furtherincludes antenna capability information separately corresponding to theN STAs, and antenna capability information of one STA is used todetermine a quantity of training sequences corresponding to the STA.

In a possible implementation, the first AP determines to perform channelsounding on the N STAs.

In a possible implementation, the trigger frame includes a quantity oftraining sequences corresponding to each of the N STAs, and a quantityof training sequences included in the channel sounding frame isspecified by the trigger frame.

In a possible implementation, a frame body of the trigger frame includesfirst information, and the first information is used to indicateinformation about the quantity of training sequences corresponding toeach of the N STAs and information about occupied bits of the quantityof training sequences corresponding to each of the N STAs.

In a possible implementation, the first information indicates that the NSTAs correspond to a same quantity of training sequences and thequantity occupies a first bit; or the first information indicates that aquantity of training sequences corresponding to information about afirst bit is ignored, the quantity of training sequences correspondingto each of the N STAs occupies a second bit, the second bit includes Nsub-bits, and one sub-bit indicates a quantity of training sequencescorresponding to one STA.

In a possible implementation, a quantity of training sequences includedin the channel sounding frames is determined by the N STAs separatelybased on the antenna capability information of the N STAs.

In a possible implementation, the trigger frame includes time points atwhich the N STAs separately send the channel sounding frames.

In a possible implementation, the first AP determines a second timepoint at which a first channel sounding frame is received, where thefirst channel sounding frame is any channel sounding frame in thechannel sounding frames separately sent by the N STAs. The first APdetermines a first time point closest to the second time point in thetime points at which the N STAs separately send the channel soundingframes. The first AP determines that a STA corresponding to the firsttime point is a STA that sends the first channel sounding frame.

In a possible implementation, that the first AP receives the channelsounding frames sequentially sent by the N STAs includes: The first APreceives, based on the time sequence of separately sending the channelsounding frames by the N STAs, the channel sounding frames sequentiallysent by the N STAs.

In a possible implementation, that the first AP receives, based on thetime sequence of separately sending the channel sounding frames by the NSTAs, the channel sounding frames sequentially sent by the N STAsincludes: The first AP determines, based on the time sequence ofseparately sending the channel sounding frames by the N STAs, the timepoints at which the N STAs separately send the channel sounding frames.For any channel sounding frame in the N channel sounding framesseparately sent by the N STAs, the first AP determines a second timepoint at which the channel sounding frame is received, and determines afirst time point closest to the second time point in the time points atwhich the N STAs separately send the channel sounding frames; determinesthat a STA corresponding to the first time point is a STA correspondingto the channel sounding frame; and obtains a quantity of trainingsequences from the STA corresponding to the channel sounding frame, anduses the quantity as a quantity of training sequences corresponding tothe STA.

In a possible implementation, the channel sounding frames separatelysent by the N STAs separately include sequence information, and thesequence information indicates a sending sequence of one channelsounding frame in the N channel sounding frames sent by the N STAs. Thatthe first AP receives, based on the time sequence of separately sendingthe channel sounding frames by the N STAs, the channel sounding framessequentially sent by the N STAs includes: For any channel sounding framein the N channel sounding frames separately sent by the N STAs, thefirst AP determines, based on sequence information of the channelsounding frame and the time sequence of separately sending the channelsounding frames by the N STAs, STA information corresponding to thesequence information in the trigger frame, determines that a STAindicated by the STA information is a STA corresponding to the channelsounding frame, obtains a quantity of training sequences from the STAcorresponding to the channel sounding frame, and uses the quantity as aquantity of training sequences corresponding to the STA.

According to a second aspect, this application provides a trainingsequence transmission method. The method includes: Second AP receive atrigger frame broadcast by a first AP, where the trigger frame indicatesa time sequence of separately sending channel sounding frames by N STAs,and N is an integer greater than 1. The second AP receive the channelsounding frames sequentially sent by the N STAs, where one channelsounding frame includes one or more training sequences. In thissolution, only one trigger frame needs to be sent, so that the N STAscan be triggered to separately report channel sounding frames to M+1APs. However, in the conventional technology, each AP needs to send oneTRQ to each STA, that is, N×(M+1) TRQs are sent in total, to triggereach STA to report a training sequence. Therefore, this solution cansignificantly reduce signaling overheads.

In a possible implementation, before the second AP receive the triggerframe broadcast by the first AP, the second AP receive indicationinformation from a central controller or the first AP, where theindication information is used to indicate to follow an indication ofthe trigger frame of the first AP.

In a possible implementation, the trigger frame includes a quantity oftraining sequences corresponding to each of the N STAs, and a quantityof training sequences included in the channel sounding frame isspecified by the trigger frame.

In a possible implementation, a frame body of the trigger frame includesfirst information, and the first information is used to indicateinformation about the quantity of training sequences corresponding toeach of the N STAs and information about occupied bits of the quantityof training sequences corresponding to each of the N STAs.

In a possible implementation, the first information indicates that the NSTAs correspond to a same quantity of training sequences and thequantity occupies a first bit; or the first information indicates that aquantity of training sequences corresponding to information about afirst bit is ignored, the quantity of training sequences correspondingto each of the N STAs occupies a second bit, the second bit includes Nsub-bits, and one sub-bit indicates a quantity of training sequencescorresponding to one STA.

In a possible implementation, a quantity of training sequences includedin the channel sounding frames is determined by the N STAs separatelybased on antenna capability information of the N STAs.

In a possible implementation, the trigger frame is further used toindicate that the second AP are ready to receive the channel soundingframes sequentially sent by the N STAs.

In a possible implementation, the trigger frame includes identifier ofthe second AP. If the second AP determine that the trigger frameincludes the identifier of the second AP, the second AP determine toreceive the channel sounding frames sequentially sent by the N STAs.

In a possible implementation, the trigger frame further includes timepoints at which the N STAs separately send the channel sounding frames.

In a possible implementation, the second AP determine a second timepoint at which a first channel sounding frame is received, where thefirst channel sounding frame is any channel sounding frame in thechannel sounding frames separately sent by the N STAs. The second APdetermine a first time point closest to the second time point in thetime points at which the N STAs separately send the channel soundingframes. The second AP determine that a STA corresponding to the firsttime point is a STA that sends the first channel sounding frame.

In a possible implementation, that the second AP receive the channelsounding frames sequentially sent by the N STAs includes: The second APreceive, based on the time sequence of separately sending the channelsounding frames by the N STAs, the channel sounding frames sequentiallysent by the N STAs.

In a possible implementation, that the second AP receive, based on thetime sequence of separately sending the channel sounding frames by the NSTAs, the channel sounding frames sequentially sent by the N STAsincludes: The second AP determine, based on the time sequence ofseparately sending the channel sounding frames by the N STAs, the timepoints at which the N STAs separately send the channel sounding frames.For any channel sounding frame in the N channel sounding framesseparately sent by the N STAs, the second AP determine a second timepoint at which the channel sounding frame is received, and determine afirst time closest to the second time point in the time points at whichthe N STAs separately send the channel sounding frames; determine that aSTA corresponding to the first time point is a STA corresponding to thechannel sounding frame; and obtain a quantity of training sequences fromthe STA corresponding to the channel sounding frame, and use thequantity as a quantity of training sequences corresponding to the STA.

In a possible implementation, the channel sounding frames separatelysent by the N STAs separately include sequence information, and thesequence information indicates a sending sequence of one channelsounding frame in the N channel sounding frames sent by the N STAs.

That the second AP receive, based on the time sequence of separatelysending the channel sounding frames by the N STAs, the channel soundingframes sequentially sent by the N STAs includes: For any channelsounding frame in the N channel sounding frames separately sent by the NSTAs, the second AP determine, based on sequence information of thechannel sounding frame and the time sequence of separately sending thechannel sounding frames by the N STAs, STA information corresponding tothe sequence information in the trigger frame; determine that a STAindicated by the STA information is a STA corresponding to the channelsounding frame; and obtain a quantity of training sequences from the STAcorresponding to the channel sounding frame, and use the quantity as aquantity of training sequences corresponding to the STA.

According to a third aspect, this application provides a trainingsequence transmission method. The method includes: A first STA receivesa trigger frame broadcast by a first AP, where the trigger frameindicates a time sequence of separately sending channel sounding framesby N STAs, the N STAs include the first STA, and N is an integer greaterthan 1. The first STA constructs a first channel sounding frame based ona quantity of training sequences corresponding to the first STA, wherethe first channel sounding frame includes one or more trainingsequences. The first STA determines a first time point for sending thefirst channel sounding frame. The first STA sends the first channelsounding frame at the first time point. Based on this solution, only onetrigger frame needs to be sent, so that the N STAs can be triggered toseparately report the channel sounding frames. However, in theconventional technology, an AP needs to send one channel trainingrequest to each STA, that is, N channel training requests are sent intotal, to trigger each STA to report a training sequence. Therefore,this solution can significantly reduce signaling overheads.

In a possible implementation, that the first STA determines a first timepoint for sending the first channel sounding frame includes: The firstSTA determines a second STA based on the time sequence of separatelysending the channel sounding frames by the N STAs, where a time sequenceof sending a channel sounding frame by the second STA is earlier than atime sequence of sending a channel sounding frame by the first STA. Thefirst STA determines, based on duration in which the second STA sendsthe channel sounding frame, the first time point for sending the firstchannel sounding frame.

In a possible implementation, the first STA determines, based on aquantity of training sequences corresponding to the second STA, theduration in which the second STA sends the channel sounding frame.

In a possible implementation, the trigger frame includes time points atwhich the N STAs separately send the channel sounding frames. That thefirst STA determines a first time point for sending the first channelsounding frame includes: The first STA obtains the first time point forsending the first channel sounding frame from the trigger frame

In a possible implementation, the trigger frame includes a quantity oftraining sequences corresponding to each of the N STAs. The first STAobtains the quantity of training sequences corresponding to the firstSTA from the trigger frame.

In a possible implementation, a frame body of the trigger frame includesfirst information, and the first information is used to indicateinformation about the quantity of training sequences corresponding toeach of the N STAs and information about occupied bits of the quantityof training sequences corresponding to each of the N STAs.

In a possible implementation, the first information indicates that the NSTAs correspond to a same quantity of training sequences and thequantity occupies a first bit; or the first information indicates that aquantity of training sequences corresponding to information about afirst bit is ignored, the quantity of training sequences correspondingto each of the N STAs occupies a second bit, the second bit includes Nsub-bits, and one sub-bit indicates a quantity of training sequencescorresponding to one STA.

In a possible implementation, the first STA determines, based on antennacapability information of the first STA, the quantity of trainingsequences corresponding to the first STA.

According to a fourth aspect, this application provides a channelsounding method. The method includes: A central controller determines NSTAs on which channel sounding needs to be performed, where N is aninteger greater than 1. The central controller sends notificationinformation to a first AP, where the notification information includesidentification information of the N STAs, and the notificationinformation is used to indicate to perform channel sounding on the NSTAs. Based on this solution, the central controller may indicate thefirst AP to perform channel sounding on the N STAs, thereby improvingchannel sounding efficiency.

In a possible implementation, the notification information furtherincludes antenna capability information separately corresponding to theN STAs, and antenna capability information of one STA is used todetermine a quantity of training sequences corresponding to the STA.

In a possible implementation, the central controller determines thefirst AP.

In a possible implementation, the central controller separately sendsindication information to M second APs, where the indication informationis used to indicate to follow an indication of a trigger frame of thefirst AP.

In a possible implementation, the central controller determines the Msecond APs.

In a possible implementation, the central controller receives theidentification information of the N STAs.

In a possible implementation, the central controller receives theantenna capability information separately corresponding to the N STAs.

According to a fifth aspect, this application provides a trainingsequence transmission apparatus. The apparatus may be an AP, or may be achip used for an AP. The apparatus has a function of implementing theembodiments of the first aspect. The function may be implemented byhardware, or may be implemented by hardware executing correspondingsoftware. The hardware or the software includes one or more modulescorresponding to the function.

According to a sixth aspect, this application provides a trainingsequence transmission apparatus. The apparatus may be an AP, or may be achip used for an AP. The apparatus has a function of implementing theembodiments of the second aspect. The function may be implemented byhardware, or may be implemented by hardware executing correspondingsoftware. The hardware or the software includes one or more modulescorresponding to the function.

According to a seventh aspect, this application provides a trainingsequence transmission apparatus. The apparatus may be a STA, or may be achip used for a STA. The apparatus has a function of implementing theembodiments of the third aspect. The function may be implemented byhardware, or may be implemented by hardware executing correspondingsoftware. The hardware or the software includes one or more modulescorresponding to the function.

According to an eighth aspect, this application provides a trainingsequence transmission apparatus. The apparatus may be a centralcontroller, or may be a chip used for a central controller. Theapparatus has a function of implementing the embodiments of the fourthaspect. The function may be implemented by hardware, or may beimplemented by hardware executing corresponding software. The hardwareor the software includes one or more modules corresponding to thefunction.

According to a ninth aspect, this application provides a trainingsequence transmission apparatus, including a processor and a memory. Thememory is configured to store computer-executable instructions. When theapparatus runs, the processor executes the computer-executableinstructions stored in the memory, so that the apparatus performs themethods according to the foregoing aspects.

According to a tenth aspect, this application provides a trainingsequence transmission apparatus, including units or means (means)configured to perform the steps in the foregoing aspects.

According to an eleventh aspect, this application provides a trainingsequence transmission apparatus, including a processor and an interfacecircuit. The processor is configured to communicate with anotherapparatus through the interface circuit, and perform the methodsaccording to the foregoing aspects. There are one or more processors.

According to a twelfth aspect, this application provides a trainingsequence transmission apparatus, including a processor, configured toconnect to a memory, and configured to invoke a program stored in thememory, to perform the methods according to the foregoing aspects. Thememory may be located inside the apparatus, or may be located outsidethe apparatus. In addition, there are one or more processors.

According to a thirteenth aspect, this application further provides acomputer-readable storage medium. The computer-readable storage mediumstores instructions; and when the instructions are run on a computer,the computer is enabled to perform the method according to the foregoingaspects.

According to a fourteenth aspect, this application further provides acomputer program product including instructions; and when the computerprogram product runs on a computer, the computer is enabled to performthe method according to the foregoing aspects.

According to a fifteenth aspect, this application further provides achip system. The chip system includes a processor, configured to performthe methods according to the foregoing aspects.

According to a sixteenth aspect, this application further provides atraining sequence transmission system, including an AP configured toperform the method according to any one of the implementations of thefirst aspect and an AP configured to perform the method according to anyone of the implementations of the second aspect.

In a possible implementation, the training sequence transmission systemfurther includes a central controller configured to perform the methodaccording to any one of the implementations of the fourth aspect.

In a possible implementation, the training sequence transmission systemfurther includes a STA configured to perform the method according to anyone of the implementations of the third aspect.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a possible network architectureaccording to this application;

FIG. 2 is a schematic diagram of another possible network architectureaccording to this application;

FIG. 3 is a schematic diagram of a training sequence transmission methodin the conventional technology;

FIG. 4 is a schematic flowchart of a training sequence transmissionmethod according to this application;

FIG. 5 is a schematic flowchart of a channel sounding method accordingto this application;

FIG. 6 is a schematic diagram in which each STA reports an NDP frame;

FIG. 7 is a format of an 802.11ax trigger frame in the conventionaltechnology;

FIG. 8 is a format of a common info field in a trigger frame;

FIG. 9 is a format of a user info field in a trigger frame;

FIG. 10 is an example of an NDP frame according to this application;

FIG. 11 is a frame format of an SDS frame according to this application;

FIG. 12 is a format of an AP info field in an SDS frame according tothis application;

FIG. 13 is a format of a user info field in an SDS frame according tothis application;

FIG. 14 is a format of an HE-SIG-A field of an NDP frame that is basedon an SDS frame according to this application;

FIG. 15 is a schematic diagram of a training sequence transmissionapparatus according to this application;

FIG. 16 is a schematic diagram of another training sequence transmissionapparatus according to this application;

FIG. 17 is a schematic diagram of still another training sequencetransmission apparatus according to this application; and

FIG. 18 is a schematic diagram of yet another training sequencetransmission apparatus according to this application.

DESCRIPTION OF EMBODIMENTS

To make objectives, technical solutions, and advantages of thisapplication clearer, the following further describes this application indetail with reference to accompanying drawings. A specific operationmethod in a method embodiment may also be applied to an apparatusembodiment or a system embodiment. In descriptions of this application,unless otherwise specified, “a plurality of” means two or more than two.

FIG. 1 is a schematic diagram of a possible network architecture towhich this application is applicable. The network architecture includesone AP and N STAs (separately referred to as a STA-1, a STA-2, . . . ,and a STA-N), and N is an integer greater than 1. The AP includes aplurality of antennas (in the figure, an example in which N antennas areincluded is used), and each STA includes one or more antennas (in thefigure, an example in which each STA includes one antenna is used). Arelationship between a quantity of antennas of the AP and quantities ofantennas of the N STAs needs to meet that the quantity of antennas ofthe AP is greater than or equal to a sum of the quantities of antennasof the N STAs. For ease of description, in FIG. 1 of this application,an example in which each STA includes one antenna, and the AP includes Nantennas is used for description.

The architecture shown in FIG. 1 may also be referred to as a multi-usermultiple-input multiple-output (MU-MIMO) technology architecture. One APmay send data to a plurality of STAs.

FIG. 2 is a schematic diagram of another possible network architectureto which this application is applicable. The network architectureincludes M+1 APs (separately referred to as an AP-1, an AP-2, . . . ,and an AP-M+1) and N STAs (separately referred to as a STA-1, a STA-2, .. . , and a STA-N), M is a positive integer, and N is an integer greaterthan 1. Each AP includes one or more antennas (in the figure, an examplein which the AP-1 includes P antennas, where P is a positive integer;and the AP-M+1 includes Q antennas, where Q is a positive integer isused). Each STA includes one or more antennas (in the figure, an examplein which each STA includes one antenna is used). A relationship betweenquantities of antennas of the M+1 APs and quantities of antennas of theN STAs needs to meet that a sum of the quantities of antennas of the M+1APs is greater than or equal to a sum of the quantities of antennas ofthe N STAs. For ease of description, in FIG. 2 of this application, anexample in which each STA includes one antenna is used for description.

There is one master AP (also referred to as a first AP in thisapplication) in the M+1 APs, and the other M APs are slave APs (alsoreferred to as second AP in this application). The master AP maybroadcast a trigger frame to each STA and each slave AP. The triggerframe is used to trigger each STA to report a channel sounding frame,and trigger each slave AP to determine whether to enter a channelsounding standby state (or referred to as a channel estimation standbystate). In other words, each slave AP is triggered to determine whetherthe slave AP is ready to receive the channel sounding frame reported byeach STA.

The architecture shown in FIG. 2 may also be referred to as a networkmultiple-input multiple-output (Network-MIMO) technology architecture. Aplurality of APs cooperate with each other by using a central controlleror under wireless control, and the plurality of APs may be virtualizedinto one AP to send a plurality of user data flows.

In this application, the AP is a device that provides a bridgingfunction between a wired network and a wireless network. Generally, oneend of the AP is connected to a backbone network in a wired manner totransfer a baseband data flow, and the other end of the AP sends thedata flow to the STA in a wireless manner by using a radio frequencyunit.

In this application, the STA is a terminal configured with a wirelesslocal area network (WLAN) function module, for example, may be a mobilephone or a notebook. It should be noted that the STA in this applicationis a non-AP STA, in other words, the STA and the AP in this applicationare different devices.

In this application, the central controller is a network device that hasa processing function, for example, a server.

To resolve problems in the technical solution in the background, asshown in FIG. 4, this application provides a training sequencetransmission method. The method may be applied to the architecture of asingle AP and a plurality of STAs shown in FIG. 1, or may be applied tothe architecture of a plurality of APs and a plurality of STAs shown inFIG. 2.

For ease of description, for the architecture shown in FIG. 1, the APmay also be referred to as a first AP. For the architecture shown inFIG. 2, one AP of the M+1 APs may be referred to as a first AP (or maybe referred to as a master AP), and the other M APs may all be referredto as second AP (or all referred to as slave APs). A unified descriptionis provided herein, and details are not described later.

The method includes the following steps.

Step 401: A first AP broadcasts a trigger frame.

The trigger frame indicates a time sequence of separately sendingchannel sounding frames by N STAs, and N is an integer greater than 1.The trigger frame is used to trigger the N STAs to construct the channelsounding frames based on a quantity of training sequences correspondingto each of the N STAs, and sequentially send the channel soundingframes.

Optionally, the trigger frame includes the quantity of trainingsequences corresponding to each of the N STAs.

Optionally, the trigger frame includes time points at which the N STAsseparately send the channel sounding frames.

For the architecture shown in FIG. 1, the first AP broadcasts thetrigger frame to the N STAs.

For the architecture shown in FIG. 2, the first AP broadcasts thetrigger frame to the N STAs and the M second APs, where M is a positiveinteger. Further, the trigger frame further indicates whether the Msecond APs are ready to receive the channel sounding frames sequentiallysent by the N STAs.

For any STA (for example, a first STA) in the N STAs, the following step402 to step 404 are performed.

Step 402: The first STA constructs a first channel sounding frame basedon a quantity of training sequences corresponding to the first STA,where the first channel sounding frame includes one or more trainingsequences.

In an implementation, if the trigger frame includes the quantity oftraining sequences corresponding to each of the N STAs, the first STAobtains the quantity of training sequences corresponding to the firstSTA from the trigger frame. For example, a quantity of trainingsequences included in the first channel sounding frame is equal to thequantity of training sequences corresponding to the first STA. Forexample, if the quantity of training sequences corresponding to thefirst STA in the trigger frame is five, the first channel sounding frameconstructed by the first STA includes five training sequences.

In another implementation, if the trigger frame does not include thequantity of training sequences corresponding to each of the N STAs, thefirst STA determines, based on antenna capability information of thefirst STA, the quantity of training sequences corresponding to the firstSTA. For example, the quantity of training sequences included in thefirst channel sounding frame is equal to a quantity of antennas of thefirst STA. For example, if the quantity of antennas of the first STA isfive, the first channel sounding frame constructed by the first STAincludes five training sequences.

Step 403: The first STA determines a first time point for sending thefirst channel sounding frame.

In an implementation, the first STA may determine a second STA based onthe time sequence of separately sending the channel sounding frames bythe N STAs, where a time sequence of sending a channel sounding frame bythe second STA is earlier than a time sequence of sending a channelsounding frame by the first STA. Then, the first STA determines, basedon duration in which the second STA sends the channel sounding frame,the first time point for sending the first channel sounding frame. Thefirst STA may determine, based on a quantity of training sequencescorresponding to the second STA, the duration in which the second STAsends the channel sounding frame. For example, the trigger frameindicates that the time sequence of separately sending the channelsounding frames by the N STAs is: a STA-1, a STA-2, . . . , and a STA-N.If the first STA is a STA-5, the STA-5 may determine, based on durationsin which the STA-1, the STA-2, a STA-3, and a STA-4 send channelsounding frames, a first time point at which the STA-5 sends the firstchannel sounding frame. If the first STA is a STA-8, the STA-8 maydetermine, based on durations in which the STA-1, the STA-2, the STA-3,the STA-4, the STA-5, a STA-6, and a STA-7 send channel sounding frames,a first time point at which the STA-8 sends the first channel soundingframe. The rest may be deduced by analogy.

In another implementation, if the trigger frame includes the time pointsat which the N STAs separately send the channel sounding frames, thefirst STA obtains the first time point for sending the first channelsounding frame from the trigger frame.

Step 404: The second AP determine, based on the trigger frame, whetherthe second AP are ready to receive the channel sounding framessequentially sent by the N STAs.

The second AP receive, in step 401, the trigger frame broadcast by thefirst AP, and optionally, the trigger frame further indicates whetherthe M second APs are ready to receive the channel sounding framessequentially sent by the N STAs. Therefore, the M second APs maydetermine, based on information indicated in the trigger frame, that theM second APs are ready to receive the channel sounding framessequentially sent by the N STAs, or are not ready to receive the channelsounding frames sequentially sent by the N STAs. For example, the secondAP may determine whether the trigger frame includes identifier of thesecond AP, to determine that whether the second AP are ready to receivethe channel sounding frames sequentially sent by the N STAs. If thetrigger frame includes the identifier of the second AP, the second APdetermine to receive the channel sounding frames sequentially sent bythe N STAs. If the trigger frame does not include the identifier of thesecond AP, the second AP determine not to receive the channel soundingframes sequentially sent by the N STAs.

Alternatively, the trigger frame does not indicate whether the M secondAPs are ready to receive the channel sounding frames sequentially sentby the N STAs. Instead, a central controller indicates whether the Msecond APs are ready to receive the channel sounding frames sequentiallysent by the N STAs.

Being ready to receive the channel sounding frames sequentially sent bythe N STAs may also be understood as entering a channel estimationstandby state or a channel sounding standby state. This solution isapplicable to a scenario in which the plurality of APs simultaneouslyperform channel sounding shown in the architecture in FIG. 2.

Being not ready to receive the channel sounding frames sequentially sentby the N STAs may also be understood as not entering the channelestimation standby state or the channel sounding standby state. Thissolution is applicable to a scenario in which only one AP (namely, thefirst AP) performs channel sounding in the architecture shown in FIG. 1.

Step 404 is an optional step.

Certainly, the trigger frame or the central controller may not indicatewhether the M second APs are ready to receive the channel soundingframes sequentially sent by the N STAs, but it is specified that all APsthat receive the trigger frame receive the channel sounding framessequentially sent by the N STAs.

Step 405: The first STA sends the first channel sounding frame at thefirst time point.

The first AP may receive the channel sounding frames sequentially sentby the N STAs. One channel sounding frame includes one or more trainingsequences, and a quantity of training sequences included in the channelsounding frame is specified by the trigger frame.

Optionally, if step 404 is performed, the M second APs may also receivethe channel sounding frames sequentially sent by the N STAs.

The first AP may sequentially receive the channel sounding framesseparately sent by the N STAs. Optionally, the first AP may determine,based on the following method, which STA sends which channel soundingframe: If the first AP receives the first channel sounding frame at asecond time point, the first AP determines a time point closest to thesecond time point in the time points at which the N STAs separately sendthe channel sounding frames, for example, the first time point, anddetermines that a STA corresponding to the first time point (namely, thefirst STA) is a STA that sends the first channel sounding frame.

For the M second APs, a correspondence between a channel sounding frameand a STA, that is, which STA sends which channel sounding frame mayalso be determined by using a same method.

In this application, the reason why which STA sends which channelsounding frame may be determined by using the method is as follows: Aninterval between the channel sounding frames that are sent by the N STAsis at least 16 (short interframe space)+40 (physical frame header)=56 μs(for details, see time calculation shown in Example 1 and Example 2).Because STAs with a closest time point need to be selected, a half ofthe 56 μs is used as a dividing line. Therefore, in wireless space, atransmission distance is 8400 m (the light speed×28 μs). An indoorwireless transmission distance is definitely less than 8400 m (a basicindoor distance is within 1000 m). Therefore, it is reliable to use thefirst time point and the second time point as the determining basis.

The foregoing implementation may also be understood as follows: Thefirst AP and the M second APs determine, based on the time sequence ofseparately sending the channel sounding frames by the N STAs, the timepoints at which the N STAs separately send the channel sounding frames.For any channel sounding frame in the N channel sounding framesseparately sent by the N STAs, the first AP and the M second APsdetermine a second time point at which the channel sounding frame isreceived, and determine a first time point closest to the second timepoint in the time points at which the N STAs separately send the channelsounding frames; determine that a STA corresponding to the first timepoint is a STA corresponding to the channel sounding frame; and obtain aquantity of training sequences from the STA corresponding to the channelsounding frame, and use the quantity as a quantity of training sequencescorresponding to the STA.

In an alternative implementation, the first AP and the M second APs mayalternatively determine, by using the following method, which STA sendswhich channel sounding frame: After receiving the trigger frame, the NSTAs may separately determine, based on the time sequence of separatelyreporting the channel sounding frames by the N STAs indicated in thetrigger frame, a sequence of reporting the channel sounding frame byeach STA. To be specific, a sequence of STA information corresponding toan association identifier of the STA in the trigger frame is recorded,and the sequence information is added when the channel sounding framesare constructed. After receiving the channel sounding frames, the firstAP and the M second APs obtain corresponding fields of the channelsounding frames to obtain the sequence of the STA, and then obtain theassociation identifier (namely, an identifier of the STA) in the STAinformation corresponding to the sequence in the trigger frame. In thisway, it can be determined which STA reports the channel sounding frame.The method may be understood as follows: For any channel sounding framein the N channel sounding frames separately sent by the N STAs, thefirst AP and the M second APs determine, based on sequence informationof the channel sounding frame and the time sequence of separatelysending the channel sounding frames by the N STAs, STA informationcorresponding to the sequence information in the trigger frame;determine that a STA indicated by the STA information is a STAcorresponding to the channel sounding frame; and obtain a quantity oftraining sequences from the STA corresponding to the channel soundingframe, and use the quantity as a quantity of training sequencescorresponding to the STA.

In another alternative implementation, the first AP and the M second APsmay alternatively determine, by using the following method, which STAsends which channel sounding frame: When the N STAs receive the triggerframe to construct the channel sounding frames, the identifier (alsoreferred to as the association identifier) of each STA may be added tothe corresponding fields of the channel sounding frames. After receivingthe channel sounding frames, the first AP and the M second APs obtainthe corresponding fields of the channel sounding frames, to obtain theassociation identifier of the STA in the channel sounding frames, thatis, determine that which STA sends the channel sounding frame. Themethod may be understood as follows: For the first channel soundingframe, the first channel sounding frame is any channel sounding frame inthe channel sounding frames separately sent by the N STAs, the firstchannel sounding frame includes STA information, and the first AP andthe M second APs determine a STA indicated by the STA information as aSTA corresponding to the first channel sounding frame.

According to the foregoing solution, the first AP broadcasts one triggerframe, so that the N STAs can be triggered to sequentially send thechannel sounding frames. After receiving the channel sounding framessequentially reported by the STAs, the first AP may separately performsounding, based on the training sequences in the channel soundingframes, on channels between the first AP and the STAs, to learn ofchannel state information between the first AP and the STAs.

Based on the foregoing solution of step 401 to step 403 and step 405,compared with a channel sounding method in the architecture of a singleAP and N STAs in the conventional technology, the solution has thefollowing beneficial effects: In this solution, only one trigger frameneeds to be sent, so that the N STAs can be triggered to separatelyreport the channel sounding frames to one AP. However, in theconventional technology, an AP needs to send one TRQ to each STA, thatis, N TRQs are sent in total, to trigger each STA to report a trainingsequence. Therefore, this solution can significantly reduce signalingoverheads.

Based on the foregoing solution of step 401 to step 405, compared with achannel sounding method in the architecture of M+1 APs and N STAs in theconventional technology, the solution has the following beneficialeffects: In this solution, only one trigger frame needs to be sent, sothat the N STAs can be triggered to separately report the channelsounding frames to the M+1 APs. However, in the conventional technology,each AP needs to send one TRQ to each STA, that is, N×(M+1) TRQs aresent in total, to trigger each STA to report a training sequence.Therefore, this solution can significantly reduce signaling overheads.

For the foregoing solution 1 based on the architecture shown in FIG. 1(namely, the solution of step 401 to step 403 and step 405) or for theforegoing solution 2 based on the architecture shown in FIG. 2 (namely,the solution of step 401 to step 405), before step 401, either of thefollowing two methods may alternatively be used to trigger execution ofthe foregoing solution 1 or solution 2. Descriptions are separatelyprovided below.

Method 1: The First AP Triggers Execution of the Foregoing Solution 1 orSolution 2.

For example, the first AP may determine STAs on which channel soundingneeds to be performed. For example, the first AP may determine thatchannel sounding needs to be performed on STAs that have data requestsor whose channel information is aged (to be specific, channelinformation obtained through sounding last time has exceeded a coherencetime when a channel does not change or a fixed time set by a system)(namely, the foregoing N STAs). Certainly, in actual application, it mayalternatively be determined that sounding needs to be performed on someSTAs in the N STAs.

Based on the solution 2 of the architecture shown in FIG. 2, before step401, the first AP may further separately send indication information tothe M second APs, where the indication information is used to indicatethe M second APs to follow an indication of the trigger frame of thefirst AP.

Method 2: The Central Controller Triggers Execution of the ForegoingSolution 1 or Solution 2.

Based on the method, before step 401, the central controller maydetermine the N STAs on which channel sounding needs to be performed,and then send notification information to the first AP, where thenotification information includes identification information of the NSTAs, and the notification information is used to indicate to performchannel sounding on the N STAs. The central controller may determinethat channel sounding needs to be performed on STAs that have datarequests or whose channel information is aged (to be specific, channelinformation obtained through sounding last time has exceeded a coherencetime when a channel does not change or a fixed time set by a system)(namely, the foregoing N STAs). Certainly, in actual application, it mayalternatively be determined that sounding needs to be performed on someSTAs in the N STAs.

Optionally, the central controller may further enable the notificationinformation to carry antenna capability information separatelycorresponding to the N STAs, and antenna capability information of oneSTA is used to determine a quantity of training sequences correspondingto the STA.

Based on the solution 2 of the architecture shown in FIG. 2, before step401, the first AP may further separately send indication information tothe M second APs, where the indication information is used to indicatethe M second APs to follow an indication of the trigger frame of thefirst AP.

Based on the solution 2, optionally, the central controller may furtherdetermine the first AP (namely, the master AP) and the M second APs(namely, the slave APs).

For example, if a STA under an AP has a data request, and a frequencychannel of the AP is not occupied, the AP is selected as an AP thatneeds to perform channel sounding. For example, finally selected APsthat need perform channel sounding are the M+1 APs.

Further, the central controller may select one first AP (namely, themaster AP) from the M+1 APs, and the other M APs serve as the second AP(namely, the slave APs). The slave APs need to follow the indication ofthe trigger frame of the master AP.

The method for selecting the first AP by the central controller includesbut is not limited to:

(1) The central controller selects the first AP based on a service. AnAP with a maximum service volume is selected as the first AP, in otherwords, STAs under the selected first AP establish a maximum quantity ofdata services.

(2) The central controller selects the first AP based on a location. Arelatively central AP is selected as the first AP, so that all APs andSTAs can receive a broadcast signal of the trigger frame.

(3) The central controller selects the first AP based on fairness. AllAPs serve as first APs in turn.

Optionally, the antenna capability information of each STA stored in thecentral controller may be reported by each AP.

Further, for the trigger frame in any one of the foregoing embodiments,in an implementation, first information may be carried in a frame bodyof the trigger frame. The first information is used to indicateinformation about the quantity of training sequences corresponding toeach of the N STAs and information about occupied bits of the quantityof training sequences corresponding to each of the N STAs. For example,the first information indicates that the N STAs correspond to a samequantity of training sequences and the quantity occupies a first bit.For another example, the first information indicates that a quantity oftraining sequences corresponding to information about the first bit isignored, the quantity of training sequences corresponding to each of theN STAs occupies a second bit, the second bit includes N sub-bits, andone sub-bit indicates a quantity of training sequences corresponding toone STA.

The following describes the foregoing solutions based on thearchitecture shown in FIG. 2 and with reference to specific examples.

FIG. 5 is a schematic flowchart of a channel sounding method accordingto this application. The method includes a training sequencetransmission method.

It should be noted that, in a procedure shown in FIG. 5, the first AP inthe foregoing examples is referred to as a master AP, and the second APin the foregoing examples are referred to as slave APs. In addition, anexample in which a channel sounding frame is an NDP frame and a trainingsequence is a high efficiency long training sequence (High EfficiencyLong Training field, HE-LTF) is used for description.

The method includes the following steps.

Step 501: N STAs separately undergo normal association andauthentication processes with M+1 APs.

In this process, each AP records identification (ID) information of theSTAs and a quantity of transmit antennas (namely, antenna capabilityinformation) included in the STAs. In the normal association process,the two pieces of information are included in information of anassociation frame.

Step 502: Each AP separately reports collection information to a centralcontroller.

The reported collection information includes the identificationinformation, the antenna capability information, and the like of theSTAs that are collected by each AP in step 501.

The central controller stores the collection information reported by theAPs, and the information may be used to determine which STAs on whichchannel sounding needs to be performed.

Step 503: The central controller notifies the master AP to startbroadcasting a trigger frame, sequentially sends identifiers(AID_(User, 1), AID_(User, 2), . . . , AID_(User, N)) of the N STAs onwhich channel sounding needs to be performed, the antenna capabilityinformation (N_(Tx, User) ₁ , N_(Tx, User) ₂ , . . . , N_(Tx, User) _(N)) of the N STAs, and identifiers (BSSID_(AP, 1), BSSID_(AP, 2), . . . ,BSSID_(AP, M)) of the M slave AP to the master AP, and further indicatesthe M slave AP that needs to perform channel sounding together to followan indication of the trigger frame of the master AP.

It should be noted that, in actual application, the central controllermay determine that channel sounding needs to be performed on all the NSTAs, or may determine that channel sounding needs to be performed onsome STAs in the N STAs. For ease of description, in this embodiment, anexample in which channel sounding needs to be performed on all the NSTAs (namely, the N STAs) is used for description.

It should be noted that, in any step before step 503, the centralcontroller may further select APs that need to perform channel soundingfrom the M+1 APs (in this embodiment of this application, an example inwhich all the M+1 APs need to perform channel sounding is used), andthen select one master AP from the M+1 APs and select the other M APs asthe slave APs. For a selection method, refer to related descriptions inthe embodiment shown in FIG. 4.

Step 504: The master AP determines the number of HE-LTFs that need to beused by the N STAs on which channel sounding needs to be performed and atime sequence of reporting NDP frames.

For example, the master AP may determine, based on the antennacapability information of the STAs, the number of HE-LTFs that need tobe used by the STAs.

For example, the master AP may self-determine the time sequence ofreporting the NDP frames by the STAs. Alternatively, the time sequenceof reporting the NDP frames by the STAs may be determined based on asequence of sending the identification information and the antennacapability information that are of the N STAs by the central controller.

Optionally, the central controller may send the number of HE-LTFs thatneed to be used by the N STAs on which channel sounding needs to beperformed and the time sequence of reporting the NDP frames to themaster AP.

Step 505: The master AP constructs the trigger frame, and broadcasts thetrigger frame to the STAs and the slave APs.

Step 506: The slave APs receive the trigger frame, determine whether toenter a channel estimation standby state, and obtain the time sequenceof reporting the NDP frames by the STAs, to determine which STA reportswhich NDP frame subsequently.

The time sequence of reporting the NDP frames by the STAs may be used todetermine a specific time point at which each STA reports the NDP frame.

Optionally, if the trigger frame includes the time point at which eachSTA reports the NDP frame, the specific time point at which each STAreports the NDP frame may be directly obtained from the trigger frame.

Step 507: The STAs receive the trigger frame, determine the number ofHE-LTFs, and construct the NDP frames based on the number of HE-LTFs.

If the trigger frame includes the number of HE-LTFs, the number ofHE-LTFs is obtained from the trigger frame. If the trigger frame doesnot include the number of HE-LTFs, the STAs determine the number ofHE-LTFs based on the antenna capability information of the STAs.

Optionally, after receiving the trigger frame, each STA determines,based on the time sequence of separately reporting the channel soundingframes by the N STAs indicated in the trigger frame, a sequence ofreporting the channel sounding frame by the STA. To be specific, asequence of STA information corresponding to an association identifierof the STA in the trigger frame is recorded, and the sequenceinformation is added to the NDP frames when the NDP frames areconstructed. Alternatively, the STA adds association identifier of theSTA (namely, an identifier of the STA) to the NDP frames.

Step 508: Each STA sends the NDP frame to the master AP and the slaveAPs based on a delay for sending the NDP frame that is calculated by theSTA.

Certainly, if the trigger frame includes the delay for sending the NDPframe by each STA, each STA does not need to calculate the delay forsending the NDP frame, but directly obtains the delay from the triggerframe.

FIG. 6 is a schematic diagram in which each STA (a value of N is 3)reports an NDP frame. In the figure, an example in which an AP-1 is amaster AP, and an AP-2 and an AP-3 are slave APs (in other words, avalue of M is 2) is used. It can be learned that each STA sequentiallyreports an NDP frame constructed by the STA.

Step 509: The master AP and the slave APs determine, based on a sequenceof the STAs in the trigger frame, the STAs that report the NDP frames,and simultaneously perform channel estimation based on the number ofHE-LTFs indicated by the STAs in the trigger frame.

The master AP and the slave APs determine, based on the time sequence ofsending the NDP frames by the STAs, the specific time point at whicheach STA reports the NDP frame.

Optionally, if the trigger frame includes the time point at which eachSTA reports the NDP frame, the AP may directly obtain the specific timepoint at which each STA reports the NDP frame from the trigger frame.

Then, the master AP and the slave APs determine, based on time points atwhich the DSP frames are received and the time points at which the STAsreport the NDP frames, which STA reports which NDP frame. For a specificimplementation, refer to related descriptions in step 405. Details arenot described herein again.

For a specific implementation in which the master AP and the slave APsperform channel estimation based on the number of HE-LTFs indicated bythe STAs in the trigger frame, refer to related descriptions in theconventional technology. Details are not described herein again.

For a specific implementation process of this step, refer to a relatedsolution in the conventional technology. Details are not describedherein again.

In the foregoing embodiment, the newly designed trigger frame has thefollowing beneficial effects:

(1) Fast and efficient self-delay implicit channel sounding isimplemented.

(2) A trigger frame may trigger all STAs on which channel sounding needsto be performed, and schedule a plurality of STAs at one time to sendNDP frames.

(3) A trigger frame may be sent by using a frame on an air interface, toindicate other APs (slave APs) to wait for and respond to NDP framessent by STAs, so that a plurality of APs simultaneously perform channelsounding, and a repeated channel sounding process of the plurality ofAPs is reduced.

(4) A STA automatically delays a corresponding time and sends NDP framesin a time sharing manner by using delay information in a trigger frame,thereby reducing frame overheads and air interface time overheads.

The following describes a process of constructing the trigger frame inthis application with reference to specific examples.

Example 1: The Trigger Frame is Designed Based on a Frame Format in theConventional Technology

In Example 1, the trigger frame may also be referred to as a triggerself-delay sounding (Trigger self-delay sounding, TSDS) frame.

FIG. 7 shows a format of an 802.11ax trigger frame in the conventionaltechnology (refer to the 802.11ax D3.2 FIG. 9-63 a). In the presentinvention, a common info (Common Info) field and a user info (User Info)field in the trigger frame are modified, and functions of other fieldsare still functions of conventional modules, to form a new triggerframe, namely, the TSDS frame in this application.

The user info field is the STA information in the foregoing embodiments,and is used to record related information of a STA.

FIG. 8 shows a format of the common info field in the trigger frameshown in FIG. 7, namely, a format of the common info field in the802.11ax trigger frame (refer to the 802.11ax D3.2 FIG. 9-63 b).

In a design of the TSDS frame in this application, the common info fieldof the trigger frame shown in FIG. 7 is modified as follows:

(1) Types of the trigger frame are added to a trigger type subfield.Table 2.1 shows modified types of the 802.11ax trigger frame.

TABLE 2.1 Types of the 802.11ax trigger frame Trigger type subfieldvalue Trigger frame variant (Trigger Type) (Trigger frame variant) 0Basic trigger frame 1 Beamforming report poll (BFRP) 2 Multi-user blockacknowledgment request 3 Multi-user request to send 4 Buffer statusreport poll (BSRP) 5 Group cast with retries multi-user blockacknowledgment request 6 Bandwidth query report poll (BQRP) 7 NDPfeedback report poll (NFRP) 8 Trigger self-delay sounding (TSDS) 9-15Reserved (Reserved)

A field before “1000” (“8” in decimal) is a reserved field. In thisapplication, “1000” (“8” in decimal) is defined to indicate the TSDSframe.

(2) A trigger dependent common info (Trigger Dependent Common Info)subfield is customized in the common info field.

The subfield may be customized, and the conventional 802.11ax triggerframe implements different functions based on the subfield to indicatehow to allocate the number of HE-LTFs in the NDP frames. This subfielddefines eight bits, namely, B64 to B71. Different values indicatedifferent operations. Table 2.2 shows customization of the triggerdependent common info subfield in the common info field of the TSDSframe in this application.

TABLE 2.2 Customization of the trigger dependent common info subfield inthe common info field of the TSDS frame Values of B64 to B71 (decimal)Description of the trigger dependent common info subfield 0 Based on thenumber of RE-LTFs indicated by B23 to B25 in the common info field, allSTAs use the same number of RE-LTFs, and the slave APs do not enter thechannel estimation standby state after receiving the TSDS frame 1 Basedon the number of RE-LTFs indicated by B23 to B25 in the common infofield, all STAs use the same number of RE-LTFs, and the slave APs enterthe channel estimation standby state after receiving the TSDS frame 2Regardless of the number of HE-LTFs indicated by B23 to B25 in thecommon info field, each STA uses the number of RE-LTFs indicated by eachuser-info SS allocation subfield, and the slave APs do not enter thechannel estimation standby state after receiving the TSDS frame 3Regardless of the number of HE-LTFs indicated by B23 to B25 in thecommon info field, each STA uses the number of RE-LTFs indicated by eachuser-info SS allocation subfield, and the slave APs enter the channelestimation standby state after receiving the TSDS frame 4-255 A BSSID APis reserved/specified for channel estimation

FIG. 9 shows a format of the user info field in the trigger frame shownin FIG. 7, namely, a format of the user info field in the 802.11axtrigger frame (refer to the 802.11ax D3.2 FIG. 9-63 e).

In the design of the TSDS frame of this application, the user info fieldof the trigger frame shown in FIG. 9 is modified as follows:

(1) The master AP assigns, based on the determined number of HE-LTFsrequired by each STA and the time sequence of reporting the NDP frames,a value to the number of spatial streams in an SS allocation/RA-RUinformation subfield indicated by B26 to B31 of each STA. The valueneeds to be equal to “N_(Tx,User) ₁ −1”.

Table 2.3 shows values of the number of spatial streams defined in thisapplication.

TABLE 2.3 Definition of the number of spatial streams Values Number ofspatial streams 0 N_(TX,User n) = 1 1 N_(TX,User n) = 2 2 N_(TX,User n)= 3 . . . . . .

For example, when the value of the number of spatial streams is 0, itindicates that the number of HE-LTFs required by a corresponding STAis 1. For another example, when the value of the number of spatialstreams is 1, it indicates that the number of HE-LTFs required by acorresponding STA is 2.

It should be noted that if all the STAs need to have the same number ofHE-LTFs, the master AP may use the number of HE-LTFs indicated by B23 toB25 in the common info field.

With reference to step 506 in the embodiment in FIG. 5, the slave APsreceive the TSDS frame, obtains a value of the trigger dependent commoninfo subfield, and determines whether to enter the channel estimationstandby state. Refer to Table 2.2. If the value of the trigger dependentcommon info subfield is 0 or 2, the slave APs determine not to enter thechannel estimation standby state. If the value of the trigger dependentcommon info subfield is 1 or 3, the slave APs determine to enter thechannel estimation standby state.

It should be noted that the slave APs herein refer to the slave APs thatfollow an indication of the TSDS frame that is sent by the master AP instep 503.

With reference to step 507 in the embodiment in FIG. 5, after receivingthe TSDS frame, the STAs first check the value of the trigger dependentcommon info subfield, determine the number of HE-LTFs, and construct theNDP frames based on the number of HE-LTFs. For example, if the value ofthe trigger dependent common info subfield is 0 or 1, all the STAsobtain the number of HE-LTFs indicated by B23 to B25 in the common infofield. For another example, if the value of the trigger dependent commoninfo subfield is 2 or 3, each STA obtains the number of HE-LTFs from theSS allocation subfield of the user-info field of the STA. Specifically,the number of HE-LTFs is obtained from the number of spatial streams inthe SS allocation subfield of the user-info field.

After obtaining the number of HE-LTFs, the STAs may construct the NDPframes based on the number of HE-LTFs. FIG. 10 shows an example of anNDP frame, namely, an HE NDP PPDU frame (refer to the 802.11ax D3.2 FIG.28-12).

A method for calculating duration of the NDP frame is as follows:

T _(NDP) =T _(L-STF) T _(L-LTF) T _(L-SIG) +T _(R-SIG) +T _(HE-SIG-A) +T_(HE-STF) +N _(HE-LTF) T _(HE-LTF) T _(PE)  (1-1)

Based on a format of the frame shown in FIG. 10, it may be furtherobtained that:

T _(NDP)=40+16*N _(HE-LTF)  (1-2)

Further, a STA whose sequence of sending the NDP frame is n (a value ofn is 1, 2, . . . , and N) (referred to as the n^(th) STA) may obtain,through calculation, a delay required for the STA to send the NDP frame.The delay is as follows:

T _(Delay)=SIFS*n+Σ _(i=1) ^(n-1)(40+16*N _(Tx,User) _(i)   (1-3)

The short interframe space SIFS is 16 μs. With reference to step 508 inthe embodiment in FIG. 5, each STA determines, based on the delayobtained through calculation, the time point for reporting the NDPframe, and then reports the NDP frame at the time point.

With reference to step 509 in the embodiment in FIG. 5, in animplementation, both the master AP and the slave APs may calculate,according to the formula (1-3), a time point at which a STA sends an NDPframe. Then, the master AP and the slave APs check, based on the timepoints at which the STAs receives the NDP frames, T_(Delay) of which STAis close to the time point, determine that the NDP frame is an NDP frameof the STA, and then perform channel estimation based on the number ofHE-LTFs carried in the NDP frame.

With reference to step 509 in the embodiment in FIG. 5, in anotherimplementation, if the NDP frame includes reported sequence information,the master AP and the slave APs may obtain the sequence information fromthe NDP frame, obtain an association identifier (namely, an identifierof a STA) in a user info field corresponding to the sequence in the TSDSframe, and determine which STA reports the NDP frame.

With reference to step 509 in the embodiment in FIG. 5, in anotherimplementation, if the NDP frame includes an identifier of a reportedSTA, the master AP and the slave APs may determine, based on theidentifier of the STA, which STA reports the NDP frame.

Example 2: The New Trigger Frame is Designed

In Example 2, the trigger frame may also be referred to as a self-delaysounding (self-delay sounding, SDS) frame.

FIG. 11 shows a frame format of an SDS frame according to thisapplication. The SDS frame is a newly added frame type. The frame needsto include only a MAC header, an AP info (AP Info) field, and a userinfo (User Info) field. Other fields are not limited. The AP info fieldand the user info field may also be added to a control frame. Thecontrol frame is not specified.

The following describes fields of the SDS frame shown in FIG. 11.

A frame control field may be any field that is not used. The field isnot specified.

A duration field indicates duration of a frame.

A BA field indicates a broadcast address, to be specific, the BA fieldindicates that the frame can be directed to all wireless devices thatcan receive the frame.

An MTA field indicates an address from which the SDS frame is sent,namely, a MAC address of the master AP in this embodiment.

An AP info field is an AP information field, mainly includes BSSIDs ofslave APs, and is used to indicate a slave AP to participate in channelestimation.

A user info field is a user information field and mainly includes AIDsof STAs, the number of HE-LTFs included in uplink NDP frames sent by theSTAs, and a time sequence for reporting the NDP frames.

FIG. 12 shows a format of the AP info field in the SDS frame accordingto this application. The AP info field needs to include only the BSSIDsof the slave APs. A quantity of slave APs is the same as a quantity ofBSSIDs. A user-defined subfield may be used for other functions, and isnot limited herein.

FIG. 13 shows a format of the user info field in the SDS frame accordingto this application. The user info field includes the following threesubfields:

(a) A subfield of an association identifier of a STA. The field is usedto identify the STA. The master AP assigns a value to BO to B11 of eachuser info field based on determined user information (namely, thedetermined identifiers of the STAs).

(b) A subfield of the number of HE-LTFs. The master AP assigns a valueto B12 to B14 of the corresponding user info field based on thedetermined number of HE-LTFs required by each STA, where the value needsto be equal to “N_(Tx,User) ₁ −1”, namely, the quantity of antennas ofthe STAs minus one. See Table 2.3. This is consistent with the foregoingcontent.

(c) A subfield of reporting time points. The master AP calculates, basedon the arranged sequence of the STAs and the number of HE-LTFs includedin the NDP frames that need to be reported by the STAs, the time pointsat which the STAs need to report the NDP frames. The calculation methodis shown in the formula (1-3) in Example 1.

The master AP converts the time points calculated by using the formulas(1-3) into binary values and assigns the binary values to B15 to B39 ofthe corresponding user info field.

It should be noted that a user-defined subfield is not limited herein,and the user-defined subfield may include any content. The user infofield needs to include only the first three subfields.

With reference to step 506 in the embodiment in FIG. 5, the slave APsreceive the trigger frame, namely, the SDS frame in this example, andcheck whether the BSSIDs in the AP info field include ID numbers of theslave APs, to determine whether the slave APs enter the channelestimation standby state. If the BSSIDs include the ID numbers, theslave APs enter the channel estimation standby state. If the BSSIDs donot include the ID numbers, the slave APs do not enter the channelestimation standby state.

It should be noted that the channel estimation standby state may bedetermined by using the AP info field of the SDS frame, or may bedirectly specified by the central controller.

After the slave APs obtain the AP info field, the slave APs obtain theuser info field, and determine reporting time points of the STAs andreporting sequence of the STAs, to determine that which STA reportswhich NDP frame. There are two methods for determining the reportingtime points: (1) The reporting time points of the corresponding STAs arecalculated based on the number of HE-LTFs of the STAs. This is the sameas the calculation method of the master AP, as shown in formulas (1 to3). (2) The delay subfield of the user info field is obtained, to obtainthe reporting time points.

It should be noted that the slave APs obtain roles of the slave APs intwo manners: (1) The SDS frame is received on an air interface, and anAP having a BSSID of the SDS frame is included in the AP info field ofthe frame. (2) A master/slave relationship is directly controlled by thecentral controller. In this case, the AP info field may be empty.

With reference to step 507 in the embodiment in FIG. 5, the STAs receivethe SDS frame, obtain the value of the user info field, determine thenumber of HE-LTFs, and construct the NDP frames.

Optionally, after receiving the SDS frame, the STAs obtain sequencescorresponding to the STAs in the user info field of the SDS frame,record the sequences, and add the sequences to HE-SIG-A fields of theNDP frames, or directly add the identifiers of the STAs, namely, theAIDs, to association identifier subfields of the HE-SIG-A fields. FIG.14 is a format of an HE-SIG-A field of an NDP frame that is based on anSDS frame. The first field may be sequence information, or may beassociation identifier information. Different functions are providedaccording to different implementations, and all fields are 12 bits.Subsequent 40 bits are not limited, and may be added as required.

Then, the STAs have two methods to obtain the time points at which theSTAs reports the constructed NDP frames: (1) Accumulated reporting timepoints are calculated based on the number of HE-LTFs of all the STAs inthe user info field, and then obtain the reporting time points of theSTAs. A calculation method is the same as that of the master AP, forexample, the formulas (1 to 3). (2) The delay subfield of the user infofield is obtained, to obtain the reporting time points. After obtainingthe reporting time points, the STAs report the NDP frames according tostep 508 in the embodiment in FIG. 5.

With reference to step 509 in the embodiment in FIG. 5, because timeperiods from times at which the STAs send the NDP frames to times atwhich the APs receive the NDP frames are generally less than 1 μs, themaster AP and the slave APs may compare a time point at which an NDPframe of a STA is received with the time points at which the STAs reportthe NDP frames (which are calculated by using the trigger frame ordirectly obtained from the trigger frame), determine that the time pointat which the NDP frame is received is close to a time point at which aSTA reports an NDP frame, in other words, determine that the NDP frameis reported by a STA with the latest time point of sending an NDP frame,and then perform channel estimation based on the number of HE-LTFscarried in the NDP frame reported by the STA.

In another determining method, the master AP and the slave APs find,based on the STA reporting sequence/association identifier subfield inthe HE-SIG-A fields in the NDP frames, the user info field of thecorresponding SDS frame, determine which STA reports the NDP frame, andthen perform channel estimation based on the number of HE-LTFs carriedin the NDP frame reported by the STA.

FIG. 15 is a possible example block diagram of a training sequencetransmission apparatus 1500 according to this application. The apparatus1500 may exist in a form of software or hardware. The apparatus 1500 mayinclude a processing unit 1502 and a communication unit 1503. In animplementation, the communication unit 1503 may include a receiving unitand a sending unit. The processing unit 1502 is configured to controland manage an action of the apparatus 1500. The communication unit 1503is configured to support communication between the apparatus 1500 andanother network entity. The apparatus 1500 may further include a storageunit 1501, configured to store program code and data of the apparatus1500.

The processing unit 1502 may be a processor or a controller, forexample, a general-purpose central processing unit (central processingunit, CPU), a general-purpose processor, a digital signal processor(digital signal processor, DSP), an application-specific integratedcircuit (application-specific integrated circuit, ASIC), a fieldprogrammable gate array (field programmable gate array, FPGA) or anotherprogrammable logic device, a transistor logic device, a hardwarecomponent, or any combination thereof. The processing unit 1502 mayimplement or execute various example logical blocks, modules, andcircuits described with reference to content disclosed in thisapplication. The processor may alternatively be a combination ofprocessors implementing a computing function, for example, a combinationof one or more microprocessors, or a combination of the DSP and amicroprocessor. The storage unit 1501 may be a memory. The communicationunit 1503 is an interface circuit of the apparatus, and is configured toreceive a signal from another apparatus. For example, when the apparatusis implemented in a form of a chip, the communication unit 1503 is aninterface circuit used by the chip to receive a signal from another chipor apparatus, or is an interface circuit used by the chip to send asignal to another chip or apparatus.

The apparatus 1500 may be an AP (for example, a first AP or second AP)in any one of the foregoing embodiments, or may be a chip used for anAP. For example, when the apparatus 1500 is the AP, the processing unit1502 may be, for example, a processor, and the communication unit 1503may be, for example, a transceiver. Optionally, the transceiver mayinclude a radio frequency circuit, and the storage unit may be, forexample, a memory. For example, when the apparatus 1500 is the chip usedfor an AP, the processing unit 1502 may be, for example, a processor,and the communication unit 1503 may be, for example, an input/outputinterface, a pin, or a circuit. The processing unit 1502 may executecomputer-executable instructions stored in the storage unit. Optionally,the storage unit is a storage unit inside the chip, for example, aregister or a buffer. Alternatively, the storage unit may alternativelybe a storage unit that is inside the AP and that is located outside thechip, for example, a read-only memory (read-only memory, ROM) or anothertype of static storage device that can store static information andinstructions, or a random access memory (random access memory, RAM).

In an embodiment, the apparatus 1500 is the first AP in the foregoingembodiments, and the communication unit 1503 of the first AP includes asending unit and a receiving unit. The sending unit is configured tobroadcast a trigger frame, where the trigger frame indicates a timesequence of separately sending channel sounding frames by N stationsSTAs, and N is an integer greater than 1. The receiving unit isconfigured to receive the channel sounding frames sequentially sent bythe N STAs, where one channel sounding frame includes one or moretraining sequences.

In a possible implementation, the sending unit is specificallyconfigured to broadcast the trigger frame to the N STAs and M secondAPs, where the trigger frame further indicates whether the M second APsare ready to receive the channel sounding frames sequentially sent bythe N STAs, and M is a positive integer.

In a possible implementation, the sending unit is further configured to:before broadcasting the trigger frame to the N STAs and the M secondAPs, separately send indication information to the M second APs, wherethe indication information is used to indicate to follow an indicationof the trigger frame of the first AP.

In a possible implementation, the receiving unit is further configuredto receive notification information from a central controller, where thenotification information includes identification information of the NSTAs, and the notification information is used to indicate to performchannel sounding on the N STAs.

In a possible implementation, the notification information furtherincludes antenna capability information separately corresponding to theN STAs, and antenna capability information of one STA is used todetermine a quantity of training sequences corresponding to the STA.

In a possible implementation, the processing unit 1502 is configured todetermine to perform channel sounding on the N STAs.

In a possible implementation, the trigger frame includes a quantity oftraining sequences corresponding to each of the N STAs, and a quantityof training sequences included in the channel sounding frame isspecified by the trigger frame.

In a possible implementation, a frame body of the trigger frame includesfirst information, and the first information is used to indicateinformation about the quantity of training sequences corresponding toeach of the N STAs and information about occupied bits of the quantityof the training sequences corresponding to each of the N STAs.

In a possible implementation, the first information indicates that the NSTAs correspond to a same quantity of training sequences and thequantity occupies a first bit; or the first information indicates that aquantity of training sequences corresponding to information about afirst bit is ignored, the quantity of training sequences correspondingto each of the N STAs occupies a second bit, the second bit includes Nsub-bits, and one sub-bit indicates a quantity of training sequencescorresponding to one STA.

In a possible implementation, a quantity of training sequences includedin the channel sounding frames is determined by the N STAs separatelybased on the antenna capability information of the N STAs.

In a possible implementation, the trigger frame includes time points atwhich the N STAs separately send the channel sounding frames.

In a possible implementation, the processing unit is further configuredto: determine a second time point at which a first channel soundingframe is received, where the first channel sounding frame is any channelsounding frame in the channel sounding frames separately sent by the NSTAs; determine a first time point closest to the second time point inthe time points at which the N STAs separately send the channel soundingframes; and determine that a STA corresponding to the first time pointis a STA that sends the first channel sounding frame.

In a possible implementation, the receiving unit is specifically toreceive, based on the time sequence of separately sending the channelsounding frames by the N STAs, the channel sounding frames sequentiallysent by the N STAs.

In a possible implementation, the processing unit 1502 is configured todetermine, based on the time sequence of separately sending the channelsounding frames by the N STAs, the time points at which the N STAs sendthe channel sounding frames; for any channel sounding frame in the Nchannel sounding frames separately sent by the N STAs, determine asecond time point at which the channel sounding frame is received, anddetermine a first time point closest to the second time point in thetime points at which the N STAs separately send the channel soundingframes; determine that a STA corresponding to the first time point is aSTA corresponding to the channel sounding frame; and obtain a quantityof training sequences from the STA corresponding to the channel soundingframe, and use the quantity as a quantity of training sequencescorresponding to the STA.

In a possible implementation, the channel sounding frames separatelysent by the N STAs separately include sequence information, and thesequence information indicates a sending sequence of one channelsounding frame in the N channel sounding frames sent by the N STAs. Theprocessing unit 1502 is specifically configured to: for any channelsounding frame in the N channel sounding frames separately sent by the NSTAs, determine, based on sequence information of the channel soundingframe and the time sequence of separately sending the channel soundingframes by the N STAs, STA information corresponding to the sequenceinformation in the trigger frame; determine that a STA indicated by theSTA information is a STA corresponding to the channel sounding frame;and obtain a quantity of training sequences from the STA correspondingto the channel sounding frame, and use the quantity as a quantity oftraining sequences corresponding to the STA.

In another embodiment, the apparatus 1500 is the second AP in theforegoing embodiments, and the communication unit 1503 of the second APincludes a sending unit and a receiving unit. The receiving unit isconfigured to: receive a trigger frame broadcast by a first AP, wherethe trigger frame indicates a time sequence of separately sendingchannel sounding frames by N STAs, and N is an integer greater than 1;and receive the channel sounding frames sequentially sent by the N STAs,where one channel sounding frame includes one or more trainingsequences.

In a possible implementation, before receiving the trigger framebroadcast by the first AP, the receiving unit is further configured toreceive indication information from a central controller or the firstAP, where the indication information is used to indicate to follow anindication of the trigger frame of the first AP.

In a possible implementation, the trigger frame includes a quantity oftraining sequences corresponding to each of the N STAs, and a quantityof training sequences included in the channel sounding frame isspecified by the trigger frame.

In a possible implementation, a frame body of the trigger frame includesfirst information, and the first information is used to indicateinformation about the quantity of training sequences corresponding toeach of the N STAs and information about occupied bits of the quantityof the training sequences corresponding to each of the N STAs.

In a possible implementation, the first information indicates that the NSTAs correspond to a same quantity of training sequences and thequantity occupies a first bit; or the first information indicates that aquantity of training sequences corresponding to information about afirst bit is ignored, the quantity of training sequences correspondingto each of the N STAs occupies a second bit, the second bit includes Nsub-bits, and one sub-bit indicates a quantity of training sequencescorresponding to one STA.

In a possible implementation, a quantity of training sequences includedin the channel sounding frames is determined by the N STAs separatelybased on antenna capability information of the N STAs.

In a possible implementation, the trigger frame is further used toindicate that the second AP are ready to receive the channel soundingframes sequentially sent by the N STAs.

In a possible implementation, the trigger frame includes identifier ofthe second AP. The processing unit 1502 is configured to: if the triggerframe includes the identifier of the second AP, determine to receive thechannel sounding frames sequentially sent by the N STAs.

In a possible implementation, the trigger frame further includes timepoints at which the N STAs separately send the channel sounding frames.

In a possible implementation, the processing unit 1502 is furtherconfigured to: determine a second time point at which a first channelsounding frame is received, where the first channel sounding frame isany channel sounding frame in the channel sounding frames separatelysent by the N STAs; determine a first time point closest to the secondtime point in the time points at which the N STAs separately send thechannel sounding frames; and determine that a STA corresponding to thefirst time point is a STA that sends the first channel sounding frame.

In a possible implementation, the receiving unit is specifically toreceive, based on the time sequence of separately sending the channelsounding frames by the N STAs, the channel sounding frames sequentiallysent by the N STAs.

In a possible implementation, the processing unit 1502 is configured to:determine, based on the time sequence of separately sending the channelsounding frames by the N STAs, the time points at which the N STAsseparately send the channel sounding frames; for any channel soundingframe in the N channel sounding frames separately sent by the N STAs,determine a second time point at which the channel sounding frame isreceived, and determine a first time point closest to the second timepoint in the time points at which the N STAs separately send the channelsounding frames; determine that a STA corresponding to the first timepoint is a STA corresponding to the channel sounding frame; and obtain aquantity of training sequences from the STA corresponding to the channelsounding frame, and use the quantity as a quantity of training sequencescorresponding to the STA.

In a possible implementation, the channel sounding frames separatelysent by the N STAs separately include sequence information, and thesequence information indicates a sending sequence of one channelsounding frame in the N channel sounding frames sent by the N STAs. Theprocessing unit 1502 is specifically configured to: for any channelsounding frame in the N channel sounding frames separately sent by the NSTAs, determine, based on sequence information of the channel soundingframe and the time sequence of separately sending the channel soundingframes by the N STAs, STA information corresponding to the sequenceinformation in the trigger frame; determine that a STA indicated by theSTA information is a STA corresponding to the channel sounding frame;and obtain a quantity of training sequences from the STA correspondingto the channel sounding frame, and use the quantity as a quantity oftraining sequences corresponding to the STA.

It may be understood that, for a specific implementation process andcorresponding beneficial effects when the apparatus 1500 is used in theforegoing training sequence transmission method, refer to relateddescriptions in the foregoing method embodiments. Details are notdescribed herein again.

FIG. 16 is a possible example block diagram of a training sequencetransmission apparatus 1600 according to this application. The trainingsequence transmission apparatus 1600 may exist in a form of software orhardware. The apparatus 1600 may include a processing unit 1602 and acommunication unit 1603. In an implementation, the communication unit1603 may include a receiving unit and a sending unit. The processingunit 1602 is configured to control and manage an action of the apparatus1600. The communication unit 1603 is configured to support communicationbetween the apparatus 1600 and another network entity. The apparatus1600 may further include a storage unit 1601, configured to storeprogram code and data of the apparatus 1600.

The processing unit 1602 may be a processor or a controller, forexample, a CPU, a general-purpose processor, a DSP, an ASIC, an FPGA oranother programmable logic device, a transistor logic device, a hardwarecomponent, or any combination thereof. The processing unit 1602 mayimplement or execute various example logical blocks, modules, andcircuits described with reference to content disclosed in thisapplication. The processor may alternatively be a combination ofprocessors implementing a computing function, for example, a combinationof one or more microprocessors, or a combination of the DSP and amicroprocessor. The storage unit 1601 may be a memory. The communicationunit 1603 is an interface circuit of the apparatus, and is configured toreceive a signal from another apparatus. For example, when the apparatusis implemented in a form of a chip, the communication unit 1603 is aninterface circuit used by the chip to receive a signal from another chipor apparatus, or is an interface circuit used by the chip to send asignal to another chip or apparatus.

The apparatus 1600 may be a STA in any one of the foregoing embodiments,or may be a chip used for a STA. For example, when the apparatus 1600 isthe STA, the processing unit 1602 may be, for example, a processor, andthe communication unit 1603 may be, for example, a transceiver.Optionally, the transceiver may include a radio frequency circuit, andthe storage unit may be, for example, a memory. For example, when theapparatus 1600 is the chip used for a STA, the processing unit 1602 maybe, for example, a processor, and the communication unit 1603 may be,for example, an input/output interface, a pin, or a circuit. Theprocessing unit 1602 may execute computer-executable instructions storedin the storage unit. Optionally, the storage unit is a storage unit inthe chip, for example, a register or a cache; or the storage unit may bea storage unit that is inside the STA and that is located outside thechip, for example, a ROM or another type of static storage device thatcan store static information and instructions, or a RAM.

In an embodiment, the apparatus 1600 is the first STA in the foregoingembodiments, and the communication unit 1603 of the first STA includes asending unit and a receiving unit. The receiving unit is configured toreceive a trigger frame broadcast by a first AP, where the trigger frameindicates a time sequence of separately sending channel sounding framesby N STAs, the N STAs include the first STA, and N is an integer greaterthan 1. The processing unit is configured to: construct a first channelsounding frame based on a quantity of training sequences correspondingto the first STA, where the first channel sounding frame includes one ormore training sequences; and determine a first time point for sendingthe first channel sounding frame. The sending unit is configured to sendthe first channel sounding frame at the first time point.

In a possible implementation, the processing unit is specificallyconfigured to: determine a second STA based on the time sequence ofseparately sending the channel sounding frames by the N STAs, where atime sequence of sending a channel sounding frame by the second STA isearlier than a time sequence of sending a channel sounding frame by thefirst STA; determine, based on duration in which the second STA sendsthe channel sounding frame, the first for sending the first channelsounding frame.

In a possible implementation, the processing unit is further configuredto determine, based on a quantity of training sequences corresponding tothe second STA, the duration in which the second STA sends the channelsounding frame.

In a possible implementation, the trigger frame includes time points atwhich the N STAs separately send the channel sounding frames. Theprocessing unit is specifically configured to obtain the first timepoint for sending the first channel sounding frame from the triggerframe.

In a possible implementation, the trigger frame includes a quantity oftraining sequences corresponding to each of the N STAs. The first STAobtains the quantity of training sequences corresponding to the firstSTA from the trigger frame.

In a possible implementation, a frame body of the trigger frame includesfirst information, and the first information is used to indicateinformation about the quantity of training sequences corresponding toeach of the N STAs and information about occupied bits of the quantityof the training sequences corresponding to each of the N STAs.

In a possible implementation, the first information indicates that the NSTAs correspond to a same quantity of training sequences and thequantity occupies a first bit; or the first information indicates that aquantity of training sequences corresponding to information about afirst bit is ignored, the quantity of training sequences correspondingto each of the N STAs occupies a second bit, the second bit includes Nsub-bits, and one sub-bit indicates a quantity of training sequencescorresponding to one STA.

In a possible implementation, the processing unit is further configuredto determine, based on antenna capability information of the first STA,the quantity of training sequences corresponding to the first STA.

It may be understood that for a specific implementation process andcorresponding beneficial effects when the apparatus 1600 is used in theforegoing training sequence transmission method, refer to relateddescriptions in the foregoing method embodiments. Details are notdescribed herein again.

FIG. 17 is a possible example block diagram of a training sequencetransmission apparatus 1700 according to this application. The trainingsequence transmission apparatus 1700 may exist in a form of software orhardware. The apparatus 1700 may include a processing unit 1702 and acommunication unit 1703. In an implementation, the communication unit1703 may include a receiving unit and a sending unit. The processingunit 1702 is configured to control and manage an action of the apparatus1700. The communication unit 1703 is configured to support communicationbetween the apparatus 1700 and another network entity. The apparatus1700 may further include a storage unit 1701, configured to storeprogram code and data of the apparatus 1700.

The processing unit 1702 may be a processor or a controller, forexample, a CPU, a general-purpose processor, a DSP, an ASIC, an FPGA oranother programmable logic device, a transistor logic device, a hardwarecomponent, or any combination thereof. The processing unit 1702 mayimplement or execute various example logical blocks, modules, andcircuits described with reference to content disclosed in thisapplication. The processor may alternatively be a combination ofprocessors implementing a computing function, for example, a combinationof one or more microprocessors, or a combination of the DSP and amicroprocessor. The storage unit 1701 may be a memory. The communicationunit 1703 is an interface circuit of the apparatus, and is configured toreceive a signal from another apparatus. For example, when the apparatusis implemented in a form of a chip, the communication unit 1703 is aninterface circuit used by the chip to receive a signal from another chipor apparatus, or is an interface circuit used by the chip to send asignal to another chip or apparatus.

The apparatus 1700 may be a central controller in any one of theforegoing embodiments, or may be a chip used for a central controller.For example, when the apparatus 1700 is the central controller, theprocessing unit 1702 may be, for example, a processor, and thecommunication unit 1703 may be, for example, a transceiver. Optionally,the transceiver may include a radio frequency circuit, and the storageunit may be, for example, a memory. For example, when the apparatus 1700is the chip used for a central controller, the processing unit 1702 maybe, for example, a processor, and the communication unit 1703 may be,for example, an input/output interface, a pin, or a circuit. Theprocessing unit 1702 may execute computer-executable instructions storedin the storage unit. Optionally, the storage unit is a storage unit inthe chip, for example, a register or a cache; or the storage unit may bea storage unit that is in the central controller and that is outside thechip, for example, a ROM or another type of static storage device thatcan store static information and instructions, or a RAM.

In an embodiment, the apparatus 1700 is the central controller, and thecommunication unit 1703 of the central controller includes a sendingunit and a receiving unit. The processing unit 1702 is configured todetermine N STAs on which channel sounding needs to be performed, whereN is an integer greater than 1. The sending unit is configured to sendnotification information to a first AP, where the notificationinformation includes identification information of the N STAs, and thenotification information is used to indicate to perform channel soundingon the N STAs.

In a possible implementation, the notification information furtherincludes antenna capability information separately corresponding to theN STAs, and antenna capability information of one STA is used todetermine a quantity of training sequences corresponding to the STA.

In a possible implementation, the processing unit is further configuredto determine the first AP.

In a possible implementation, the sending unit is further configured toseparately send indication information to M second APs, where theindication information is used to indicate to follow an indication of atrigger frame of the first AP.

In a possible implementation, the processing unit is further configuredto determine the M second APs.

In a possible implementation, the receiving unit is configured toreceive the identification information of the N STAs.

In a possible implementation, the receiving unit is further configuredto receive the antenna capability information separately correspondingto the N STAs.

It may be understood that for a specific implementation process andcorresponding beneficial effects when the apparatus 1700 is used in theforegoing training sequence transmission method, refer to relateddescriptions in the foregoing method embodiments. Details are notdescribed herein again.

FIG. 18 is a schematic diagram of a training sequence transmissionapparatus 1800 according to this application. The training sequencetransmission apparatus 1800 may be the foregoing STA (for example, thefirst STA), the AP (for example, the first AP or the second AP), or thecentral controller. The apparatus 1800 includes a processor 1802, acommunication interface 1803, and a memory 1801. Optionally, theapparatus 1800 may further include a communication line 1804. Thecommunication interface 1803, the processor 1802, and the memory 1801may be connected to each other through the communication line 1804. Thecommunication line 1804 may be a peripheral component interconnect(peripheral component interconnect, PCI for short) bus, an extendedindustry standard architecture (extended industry standard architecture,EISA for short) bus, or the like. The communication line 1804 may beclassified into an address bus, a data bus, a control bus, and the like.For ease of representation, only one thick line is used to represent thebus in FIG. 18, but this does not mean that there is only one bus oronly one type of bus.

The processor 1802 may be a CPU, a microprocessor, an ASIC, or one ormore integrated circuits configured to control program execution in thesolutions of this application.

The communication interface 1803 uses any transceiver-type apparatus, tocommunicate with another device or a communication network, for example,the Ethernet, a radio access network (radio access network, RAN), awireless local area network (wireless local area network, WLAN), or awired access network.

The memory 1801 may be a ROM or another type of static storage devicethat can store static information and instructions, or a RAM or anothertype of dynamic storage device that can store information andinstructions; or may be an electrically erasable programmable read-onlymemory (electrically erasable programmable read-only memory, EEPROM), acompact disc read-only memory (compact disc read-only memory, CD-ROM) oranother compact disc storage, an optical disc storage (including acompact disc, a laser disc, an optical disc, a digital versatile disc, aBlu-ray disc, or the like), a magnetic disk storage medium or anothermagnetic storage device, or any other medium that can be used to carryor store expected program code in a form of an instruction or a datastructure and that can be accessed by a computer, but is not limitedthereto. The memory may exist independently, and is connected to theprocessor through the communication line 1804. The memory mayalternatively be integrated with the processor.

The memory 1801 is configured to store computer-executable instructionsfor executing the solutions of this application, and execution iscontrolled by the processor 1802. The processor 1802 is configured toexecute the computer-executable instructions stored in the memory 1801,to implement the training sequence transmission method provided in theforegoing embodiments of this application.

Optionally, the computer-executable instructions in this embodiment ofthis application may also be referred to as application program code.This is not specifically limited in this embodiment of this application.

A person of ordinary skill in the art may understand that variousreference numerals such as “first” and “second” in this application aremerely used for differentiation for ease of description, and are notused to limit the scope of the embodiments of this application, orrepresent a sequence. The term “and/or” describes an associationrelationship for describing associated objects and represents that threerelationships may exist. For example, A and/or B may represent thefollowing three cases: Only A exists, both A and B exist, and only Bexists. The character “/” generally indicates an “or” relationshipbetween the associated objects. The term “at least one” means one ormore. The term “at least two” means two or more. The term “at leastone”, “any one”, or a similar expression thereof means any combinationof these items, including a single item (piece) or any combination of aplurality of items (pieces). For example, at least one (piece, or type)of a, b, or c may represent: a, b, c, a and b, a and c, b and c, or a,b, and c, where a, b, and c may be singular or plural. The term “aplurality of” means two or more, and another quantifier is similar tothis. In addition, an element (element) that appears in singular forms“a”, “an”, and “the” does not mean “one or only one” unless otherwisespecified in the context, but means “one or more”. For example, “adevice” means one or more such devices.

All or some of the foregoing embodiments may be implemented by usingsoftware, hardware, firmware, or any combination thereof. When thesoftware is used to implement the embodiments, all or some of theembodiments may be implemented in a form of a computer program product.The computer program product includes one or more computer programinstructions. When the computer program instructions are loaded andexecuted on a computer, all or some of the procedures or functionsaccording to the embodiments of this application are generated. Thecomputer may be a general-purpose computer, a special-purpose computer,a computer network, or another programmable apparatus. The computerprogram instructions may be stored in a computer-readable storage mediumor may be transmitted from a computer-readable storage medium to anothercomputer-readable storage medium. For example, the computer programinstructions may be transmitted from a website, computer, server, ordata center to another website, computer, server, or data center in awired (for example, a coaxial cable, an optical fiber, or a digitalsubscriber line (DSL)) or wireless (for example, infrared, radio, ormicrowave) manner. The computer-readable storage medium may be anyusable medium accessible by a computer, or a data storage device, forexample, a server or a data center, integrating one or more usablemedia. The usable medium may be a magnetic medium (for example, a floppydisk, a hard disk, or a magnetic tape), an optical medium (for example,a DVD), a semiconductor medium (for example, a solid state disk (SolidState Disk, SSD)), or the like.

The various illustrative logical units and circuits described in theembodiments of this application may implement or operate the describedfunctions through a general-purpose processor, a digital signalprocessor, an application-specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or another programmable logicalapparatus, a discrete gate or transistor logic, a discrete hardwarecomponent, or a design of any combination thereof. The general-purposeprocessor may be a microprocessor. Optionally, the general-purposeprocessor may alternatively be any conventional processor, controller,microcontroller, or state machine. The processor may alternatively beimplemented by a combination of computing apparatuses, such as a digitalsignal processor and a microprocessor, a plurality of microprocessors,one or more microprocessors in combination with a digital signalprocessor core, or any other similar configuration.

Steps of the methods or algorithms described in the embodiments of thisapplication may be directly embedded into hardware, a software unitexecuted by a processor, or a combination thereof. The software unit maybe stored in a RAM, a flash memory, a ROM, an EPROM, an EEPROM, aregister, a hard disk, a removable magnetic disk, a CD-ROM, or a storagemedium of any other form in the art. For example, the storage medium maybe connected to the processor, so that the processor can readinformation from the storage medium and write information into thestorage medium. Optionally, the storage medium may alternatively beintegrated into the processor. The processor and the storage medium maybe disposed in an ASIC.

These computer program instructions may alternatively be loaded onto acomputer or another programmable data processing device, so that aseries of operations and steps are performed on the computer or theanother programmable device, to generate computer-implementedprocessing. Therefore, the instructions executed on the computer or theanother programmable device provide steps for implementing a specifiedfunction in one or more processes in the flowcharts and/or in one ormore blocks in the block diagrams.

Although this application is described with reference to specificfeatures and the embodiments thereof, it is clear that variousmodifications and combinations may be made to them without departingfrom the spirit and scope of this application. Correspondingly, thespecification and accompanying drawings are merely descriptions ofexamples of this application defined by the appended claims, and areconsidered as any of or all modifications, variations, combinations, orequivalents that cover the scope of this application. It is clear that aperson skilled in the art can make various modifications and variationsto this application without departing from the scope of thisapplication. This application is intended to cover these modificationsand variations of this application provided that these modifications andvariations fall within the scope of the claims of this application andequivalent technologies of these modifications and variations.

What is claimed is:
 1. A training sequence transmission method,comprising: receiving, by a first station (STA), a trigger framebroadcast by a first access point (AP), wherein the trigger frameindicates a time sequence of separately sending channel sounding framesby N STAs, the N STAs comprise the first STA, and N is an integergreater than 1; constructing, by the first STA, a first channel soundingframe based on a quantity of training sequences corresponding to thefirst STA, wherein the first channel sounding frame comprises one ormore training sequences; determining, by the first STA, a first timepoint for sending the first channel sounding frame based on the timesequence; and sending, by the first STA, the first channel soundingframe at the first time point.
 2. The method according to claim 1,wherein the determining, by the first STA, the first time point forsending the first channel sounding frame comprises: determining, by thefirst STA, a second STA based on the time sequence of separately sendingthe channel sounding frames by the N STAs, wherein a time of sending asecond channel sounding frame by the second STA precedes a time ofsending a first channel sounding frame by the first STA; anddetermining, by the first STA based on a duration in which the secondSTA sends the second channel sounding frame, the first time point forsending the first channel sounding frame.
 3. The method according toclaim 2, further comprising: determining, by the first STA based on aquantity of training sequences corresponding to the second STA, theduration of time in which the second STA sends the second channelsounding frame.
 4. The method according to claim 1, wherein the triggerframe comprises time points at which the N STAs separately send thechannel sounding frames; and the determining, by the first STA, a firsttime point for sending the first channel sounding frame comprises:obtaining, by the first STA, the first time point for sending the firstchannel sounding frame from the trigger frame.
 5. The method accordingto claim 1, wherein the trigger frame comprises a quantity of trainingsequences corresponding to each of the N STAs; and the method furthercomprises: obtaining, by the first STA, the quantity of trainingsequences corresponding to the first STA from the trigger frame.
 6. Atraining sequence transmission method, comprising: broadcasting, by afirst access point (AP), a trigger frame, wherein the trigger frameindicates a time sequence of separately sending channel sounding framesby N stations (STAs), and N is an integer greater than 1; and receiving,by the first AP, the channel sounding frames sequentially sent by the NSTAs, wherein one channel sounding frame comprises one or more trainingsequences.
 7. The method according to claim 6, wherein the broadcasting,by a first AP, a trigger frame comprises: broadcasting, by the first AP,the trigger frame to the N STAs and M second AP, wherein the triggerframe further indicates whether the M second AP are ready to receive thechannel sounding frames sequentially sent by the N STAs, and M is apositive integer.
 8. The method according to claim 7, wherein before thebroadcasting, by the first AP, the trigger frame to the N STAs and Msecond AP, the method further comprises: separately sending, by thefirst AP, indication information to the M second AP, wherein theindication information is used to indicate to follow an indication ofthe trigger frame of the first AP.
 9. A training sequence transmissionmethod, comprising: receiving, by a second access point (AP), a triggerframe broadcast by a first AP, wherein the trigger frame indicates atime sequence of separately sending channel sounding frames by Nstations (STAs), and N is an integer greater than 1; and receiving, bythe second AP, the channel sounding frames sequentially sent by the NSTAs, wherein one channel sounding frame comprises one or more trainingsequences.
 10. The method according to claim 9, wherein before thereceiving, by second AP, a trigger frame broadcast by a first AP, themethod further comprises: receiving, by the second AP, indicationinformation from a central controller or the first AP, wherein theindication information is used to indicate to follow an indication ofthe trigger frame of the first AP.
 11. The method according to claim 9,wherein the trigger frame comprises a quantity of training sequencescorresponding to each of the N STAs, and a quantity of trainingsequences comprised in the channel sounding frame is specified by thetrigger frame.
 12. The method according to claim 9, wherein the triggerframe comprises an identifier of the second AP, and the trigger frame isfurther used to indicate that the second AP should be ready to receivethe channel sounding frames sequentially sent by the N STAs; and themethod further comprises: determining, by the second AP, that thetrigger frame comprises the identifier of the second AP; and inresponse, determining, by the second AP, to receive the channel soundingframes sequentially sent by the N STAs.
 13. The method according toclaim 9, wherein the trigger frame further comprises time points atwhich the N STAs separately send the channel sounding frames.
 14. Themethod according to claim 9, wherein the receiving, by the second AP,the channel sounding frames sequentially sent by the N STAs comprises:receiving, by the second AP based on the time sequence of separatelysending the channel sounding frames by the N STAs, the channel soundingframes sequentially sent by the N STAs.
 15. The method according toclaim 14, wherein the receiving, by the second AP based on the timesequence of separately sending the channel sounding frames by the NSTAs, the channel sounding frames sequentially sent by the N STAscomprises: determining, by the second AP based on the time sequence ofseparately sending the channel sounding frames by the N STAs, the timepoints at which the N STAs separately send the channel sounding frames;and for any channel sounding frame in the N channel sounding framesseparately sent by the N STAs, determining, by the second AP, a secondtime point at which the channel sounding frame is received, anddetermining a first time point closest to the second time point in thetime points at which the N STAs separately send the channel soundingframes; determining that a STA corresponding to the first time point isa STA corresponding to the channel sounding frame; and obtaining aquantity of training sequences from the STA corresponding to the channelsounding frame, and using the quantity as a quantity of trainingsequences corresponding to the STA.
 16. A training sequence transmissionapparatus, wherein the training sequence transmission apparatus is usedin a first station (STA) and comprises: a receiving unit, configured toreceive a trigger frame broadcast by a first access point (AP), whereinthe trigger frame indicates a time sequence of separately sendingchannel sounding frames by N STAs, the N STAs comprise the first STA,and N is an integer greater than 1; a processing unit, configured to:construct a first channel sounding frame based on a quantity of trainingsequences corresponding to the first STA, wherein the first channelsounding frame comprises one or more training sequences; and determine afirst time point for sending the first channel sounding frame based onthe time sequence; and a sending unit, configured to send the firstchannel sounding frame at the first time point.
 17. The apparatusaccording to claim 16, wherein the processing unit is further configuredto: determine a second STA based on the time sequence of separatelysending the channel sounding frames by the N STAs, wherein a time ofsending a second channel sounding frame by the second STA precedes atime of sending a first channel sounding frame by the first STA; anddetermine, based on a duration in which the second STA sends the secondchannel sounding frame, the first time point for sending the firstchannel sounding frame.
 18. The apparatus according to claim 17, whereinthe processing unit is further configured to determine, based on aquantity of training sequences corresponding to the second STA, theduration of time in which the second STA sends the second channelsounding frame.
 19. The apparatus according to claim 16, wherein thetrigger frame comprises time points at which the N STAs separately sendthe channel sounding frames; and the processing unit is furtherconfigured to obtain the first time point for sending the first channelsounding frame from the trigger frame.
 20. The apparatus according toclaim 16, wherein the trigger frame comprises a quantity of trainingsequences corresponding to each of the N STAs; and the processing unitis further configured to obtain the quantity of training sequencescorresponding to the first STA from the trigger frame.